Currently, commercially available secondary batteries comprise nickel cadmium, nickel hydrogen, nickel zinc and lithium secondary batteries. Among them, lithium secondary batteries have drawn much attention because of little memory effect to allow unrestrained charging/discharging, as well as very low self-discharging rate and high energy density, compared to nickel-based secondary batteries.
For such secondary batteries, lithium-based oxides and carbon materials are mainly used respectively as positive electrode active materials and negative electrode active materials. A lithium secondary battery comprises an electrode assembly, which consists of a positive plate and a negative plate, with a separator therebetween, to which such positive electrode and negative electrode active materials are applied respectively, and an exterior material, i.e., a battery case, which stores and seals the electrode assembly along with an electrolyte.
Generally, lithium secondary batteries can be classified into a can-type secondary battery which integrates an electrode assembly into a metal can, and a pouch-type secondary battery which integrates an electrode assembly into a pouch made of an aluminum laminate sheet.
Recently, secondary batteries are widely used in middle- or large-sized devices like vehicles and power storage devices as well as small-sized devices like portable electronic appliance. When used in such middle- or large-sized devices, a plurality of secondary batteries are electrically connected in large numbers to increase the capacity and output. Especially, in such middle- or large-sized devices, pouch-type secondary batteries are usually employed because they can easily be stacked.
However, pouch-type secondary batteries are typically packaged in a battery case made of an aluminum/polymer resin laminate sheet, thus exhibiting insufficient mechanical rigidity. Therefore, when manufacturing a battery module with a plurality of pouch-type secondary batteries, frames are often employed to protect such secondary batteries from external shock, inhibit the movement thereof, and allow easy stacking.
Frames can be substituted for by other various terms such as cartridge, and are usually arranged in the shape of a rectangular plate with the center being empty, with the four sides encompassing the outer peripheral portions of pouch-type secondary batteries. In order to manufacture a battery module, a plurality of such frames are stacked and secondary batteries can be placed in inner empty spaces formed thereby.
On the other hand, when assembling a plurality of secondary batteries using such a plurality of frames, a plate-shaped cooling pin can be interposed between the plurality of secondary batteries. Secondary batteries may be used in high-temperature environment such as in summer, and may generate heat on their own. In this case, when a plurality of secondary batteries are stacked on each other, the temperature of secondary batteries can be increased higher; and if the temperature becomes higher than suitable levels, the performance of secondary batteries may be deteriorated, even with the risk of explosion or fire in worse cases. Therefore, when arranging a battery module, a cooling pin is usually interposed between secondary batteries to prevent a rise in the temperature of secondary batteries.
Such a cooling pin is plate-shaped to be called a cooling plate, which is placed between secondary batteries in a battery module to cool secondary batteries in various forms and manners. Among such forms and manners to cool secondary batteries, air-cooling is typically and widely used to lower the temperature of secondary batteries via heat exchange between a cooling plate and air by allowing external air to flow around the cooling plate.
For a battery module cooling secondary batteries through air-cooling, it is important to ensure a channel around cooling plates stably and thus allow external air to flow smoothly through such a channel. For conventional battery modules, however, it is difficult to ensure a channel around cooling plates stably. Especially, aluminum material is widely used in cooling plates, which are liable to deformations such as being pressed or warped while frames to stack are discharged during injection molding or coupled with other frames, or battery modules are used.
Such deformations of cooling plates may constrict or block a channel, disrupting the flow of external air through a channel and thereby deteriorating cooling efficiency for secondary batteries through cooling plates. While some configurations such as beads formed on cooling plates in order to prevent such deformations have been suggested, they still cannot ensure a channel stably because such beads themselves may also be deformed.